Method of joining plastic elements



July 28, 1953 w. K. SMITH METHOD OF JOINING PLASTIC ELEMENTS Filed June16, 1947 INVENTOR.

PWLTERKLW/m ATTORNEYS.

Patented July 28, 1953 METHOD OF JOINING PLASTIC ELEMENTS Walter K.Smith, Pottstown, Pa., assignor to The Firestone Tire & Rubber Company,Akron, Ohio, a corporation of Ohio Application June 16, 1947, Serial No.754,958

1 Claim.

This invention relates to an improved method of heat sealing seams inplastic material.

An important object of the invention resides in the provision of animproved method for providing sealing seams in material such as plasticleather during manufacture of articles therefrom.

A more specific object of the invention is to provide a method ofrapidly joining contiguous elements of thermoplastic material throughthe employment of electrical energy.

Another object of the invention is to provide an improved method andapparatus for securely bonding a pair of contiguously disposedthermoplastic elements while confining said bond to a determinate localarea thereof, as for example, to a narrow seam.

A further object of the invention is to provide suitable means forcarrying out the method above described.

Other objects and advantages will become apparent to persons skilled inthe art upon examination of the drawings, the description, and theappended claim.

In the drawings:

Fig. 1 is a diagrammatic view of apparatus particularly adapted forcarrying out the method of bonding;

Fig. 2 is a view taken along line 2-2 of Fig. 1 illustrating a pair ofcontiguously disposed elements to be joined in accordance with theprinciples of the invention;

Fig. 3 illustrates the elements shown in Fig. 2 bonded together alongthe scam in the manner taught herein; and

Fig. 4 is a fragmentary section taken along line 4-4 of Fig. 3.

The increased popularity of so-called plastic material during the pastfew years has resulted in the widespread use of that material inmanfactured articles. While the word plastic may be used to designate. athermosetting material, it is widely applied to various materialspossessing properties of thermoplasticity. The present invention isconcerned with the latter type of material. For example, many articlesenjoying wide current popularity are derived from polyvinyl chloridebase resins and possess thermoplastic characteristics. This material isemployed in socalled plastic leather which may consist of a film ofpolyvinyl chloride calendered to a fabric base and embossed. It may notnecessarily be backed by fabric or embossed. Plastic leather, in theform most widely adopted at the present time, is embossed to resemblenatural leather.

This material is currently manufactured into handbags, wallets and manyother items. The necessity of providing suitable bonding, especially inthe form of seams, during manufacture of the finished article withoutsubstantial disfigurement of the embossed design, has presented adifficult manufacturing problem which is satisfactorily solved by thepresent invention.

As best shown in Figs. 1 and 2, a pair of plastic leather sheets l0 andH to be joined along a seam are placed intermediate slabs or blocks l4and It of dielectric material such as, for example, a composition ofasbestos fiber and Portland cement known in the trade as Transite.During assembling of the unit shown in Fig. 2, an electricallyconductive wire [8, preferably of Nichrome, is placed intermediate thethermoplastic elements It and H to assume the pattern of a desired seam.As shown in Fig. 1, wire I 8 is placed in a position to define a seamrunning parallel to the side margins of the two pieces of plasticleather. If it is desirable to minimize or eliminate the raised ribportion appearing on the outer surfaces of the sheets when ordinaryNichrome wire i8 is used, the wire may be flattened. Nichrome wire of.020" diameter, flattened, has been successfully employed for thispurpose. The ends 20 and 2| of wire l8 are connected by lines 22 and 23to a variable transformer or variac 25, which in turn is connected to asuitable source of alternating current as shown. Adjustment of variac 25controls the heating of Nichrome wire l8 to any desired degree.

Prior to application of the heating current, slabs l4 and It may beplaced under suitable pressure, if required. It may be found that withcertain material and certain size wire, the pull of gravity on block itwill suffice to effect the proper seal. Upon application of the heatingcurrent to a degree to render the material of elements Ill and Itfusible in the area immediately adjacent wire [3, a sufficient amount ofpressure should exist between blocks I 4 and I6 to move elements l0 andI l into contiguous relation throughout the area adjacent wire [8 toform an effective bond between the elements with wire l8 completelyembedded in the thermoplastic material.

It has been found that good results are obtained if the variabletransformer is operated in a manner rapidly to bring the wire to a redheat for only an instant. Sufiicient heat is provided in this manner tomelt the plastic material to a. point enabling blocks l4 and It to movetogether to bring elements l0 and I l into bonded engagement.

The above methods avoid destruction of the embossed pattern whichoccurred during unsuccessful attempts to effect a bond by applying heatfrom a torch or burner, and if desired, a ridge or bead may be providedon the enjoined surfaces of elements I!) and II, the extent of said ribbeing dependent upon the dimensions of wire I8. It is often desirable inthe manufacture of certain articles to produce ribs for design purposes.

Upon completion of the bonding operation, the wire I8 is of course leftin the material to add strength and rigidity through the area of theseam, wire l8 being trimmed off as desired. It is apparent that wire 18may readily be disposed in a configuration to produce the desired bond,internal reenforcement or artistic pattern.

What is claimed is:

The method of bonding an element of thermoplastic material to a secondthermoplastic element, one of said elements having the form of arelatively thin sheet of material, which comprises placing a metallicwire between said elements, subjecting said elements to pressure toforce them together, and electrically heating the wire to cause theelements to fuse and to bond together adjacent the wire embedding thewire in the elements, aid sheet being molded about the wire to assumethe shape of the wire forming an ornamental rib on the external surfaceof the sheet.

WALTER K. SMITH.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 370,091 Scarles Sept. 20, 1887 1,080,990 Meyercord Dec. 9,1913 1,339,736 Burke May 11, 1920 1,350,281 Lynah Aug. 17, 19201,960,120 Mohring May 22, 1934 2,089,469 Dix Aug. 10, 1937 2,241,312Luty May 6, 1941 2,340,510 Corley Feb. 1, 1944 2,372,929 Blessing Apr.3, 1945 2,378,301 Sidell June 19, 1945 2,387,227 Andersen Oct. 23, 19452,393,100 Gallay Jan. 15, 1946 2,422,725 Gilfillan June 24, 19472,477,267 Robinson July 26, 1949 2,489,867 DOrio Nov. 29, 1949 FOREIGNPATENTS Number Country Date 522,524 Great Britain June 20, 1940

